The present invention relates to an adjustable seal assembly for maintaining a fluid tight seal in a vessel, and more particularly, to a method and apparatus for forming an adjustable seal between two sections of a vacuum vessel wherein the adjustable seal is adapted to withstand relative axial motion between the two sections of the vessel,
Most vacuum vessels in use today are made of metal or composite materials. Where it is necessary to maintain an adjustable seal or adjustable boundary between a vacuum chamber of the vessel and an area of atmospheric or other non-vacuum pressure, such vacuum vessels that are made of metal typically utilize a metallic bellows formed between two sections of the vessel. The metallic bellows functions as the adjustable boundary between the vacuum portion and non-vacuum portion because the metallic bellows is adapted to move in a prescribed direction, i.e. an axial direction, through the accordion type movement of the bellows. This axial movement allows for the displacement of one section of the vessel relative to the second section of the vessel. Typically, the metallic bellows is easily attached to both sections of a metal vessel and thus forms an adjustable yet fluid tight seal between the vacuum portion of the vessel and the non-vacuum portion.
Where the vessel is fabricated from a composite material, as is the case for selected vessels in electron microscopes, satellites, and other airborne vehicles, the use of a metallic bellows is not always feasible. This is due primarily to the different materials used in the construction of the metallic bellows and the composite vessel which ultimately affects the reliability and maintainability of the vessel. For example, the use of a metallic bellows within a composite vessel presents certain difficulties in forming a fluid tight attachment between the metal bellows and composite sections of the vessel during the vessel fabrication process.
An alternate form of an adjustable seal is the rolling seal or rolling diaphragm as disclosed in several related patents. For example, in U.S. Pat. No. 3,722,506 issued Mar. 27, 1973 (McMillian, Jr.), there is shown a U-shaped rolling seal adapted for use between a piston and cylinder in a spirometer. As disclosed, this U-shaped rolling seal can only be used with devices having a circular shape or cross-section. In addition, the disclosed U-shaped rolling seal is not suited for use within vacuum vessels or other devices where the adjustable seal encounters moderately high forces. More importantly, the disclosure specifically avoids using any fibers or reinforcing material in the U-shaped rolling seal due to concerns of friction or hysteresis during movement of the rolling seal.
An alternative form of an adjustable seal is disclosed in U.S. Pat. No. 3,856,335, issued Dec. 24, 1974 (Blake). This related art reference discloses a rolling annular diaphragm which forms a fluid-tight slip joint between two casing members for absorbing shock energy between through the rolling movement of the annular diaphragm. Yet another rolling diaphragm seal between two parts adapted to move relative to one another is disclosed in U.S. Pat. No. 3,934,480, issued Jan. 27, 1976 (Nederlof). As with the other described related art, this particular rolling diaphragm seal is only suited for use with a piston and cylinder combination or other annular shaped cooperating parts. See also U.S. Pat. No. 2,920,908 issued Jan. 12, 1960 (Mitchell) which shows an annular seal made of Neoprene synthetic rubber for sealing the region between the exterior surface of a pipeline and a surrounding cylindrical casing, and U.S. Pat. No. 3,416,819 issued Dec. 17, 1968 (Day) which utilizes a silicon rubber elastomer as part of an assembly to seal a transition region between two pipes thereby creating a fluid-tight joint regardless of relative axial movement of the two pipes.
None of the aforementioned related art seals, however, are adapted for use in non-circular devices or vessels. In addition, none of the aforementioned related art seals are suitable for use in a vacuum environment, high purity environment, or other stringent environment especially where there is only a very thin gap between the moving components. What is needed therefore, is an adjustable seal assembly that can be used in vessels of circular as well as non-circular cross sections. More importantly, there is needed a very thin adjustable seal assembly suitable for use in a vacuum vessel or any other vessel where the seal is subjected to moderately high pressure differences and other stringent environments.